The present invention relates to a radiographic imaging system for taking a radiographic image of an examinee and more particularly to a radiographic imaging system whereby the examinee is allowed to know the progress of imaging session as in long region imaging where a series of successive images are taken.
A radiographic image detector has been conventionally used in medicine to produce diagnostic images or in industry to conduct nondestructive tests. The radiographic image detector converts radiation that has penetrated a subject into an electric signal to achieve radiographic imaging. The radiation here includes X-ray, alpha ray, beta ray, gamma ray, electron beam, and ultraviolet ray.
The radiographic image detector is exemplified by a solid state radiation detector, i.e., so-called a flat panel detector hereinafter referred to as FPD, which converts radiation into an electric image signal, and an X-ray image tube that converts a radiographic image into a visible image.
In a radiographic imaging system using an FPD, a subject is irradiated with radiation emitted from a radiation source, whereupon the FPD converts the radiation that has penetrated the subject into an electric signal, and the electric signal corresponding to image data of the subject is read out from the FPD to produce a radiographic image.
To permit appropriate and efficient operations of such a radiographic imaging system, various propositions have been made to allow the operator (medical doctor or radiologist) to know the state of the imaging system and the conditions of the imaging session.
For example, JP 2005-65940 A discloses a radiographic imaging system (X-ray imaging system) comprising an imaging preparation switch and an imaging switch,as well as a hand switch that is removable from an operation panel, wherein the hand switch emits green light upon completion of preparation of the system for imaging in response to depression of the imaging preparation switch and emits orange light upon completion of imaging by the system in response to depression of the imaging switch, thereby notifying the operator of the state of the system and the progress of the imaging session.
US 2005/0220269 A1 discloses a radiographic imaging system provided with two operation periods, one of which is an idle operation period in which a readout interval for idle readout performed to remove a residual image prior to exposure alternates repeatedly with a wait interval during which exposure is possible, the other being a readout period for a post-exposure readout. In this system, immediately after the beginning of the wait period, an exposure guide signal through sound, light, vibration, etc. is generated indicating that exposure is possible to allow the operator to effect exposure at an appropriate timing in the idle operation period.
Such a radiographic imaging system typically performs imaging (normal imaging) such that an image is taken of the examinee, holding still, by a single exposure (irradiation).
Also known is an imaging method, such as long region imaging and tomosynthesis imaging, whereby a plurality of images are successively taken of (or images are successively taken by scanning) an examinee, who is asked to stay motionless, by changing the imaging position (imaging region) or the imaging angle (radiation emission angle).
Long region imaging is an imaging method for taking radiographic images of a long region that is longer than the imaging surface of the FPD such as the whole region of a spine (the whole spine) and the whole region of lower extremities (the whole lower extremities).
Presently, a typical FPD measures only about 43 cm×43 cm. Therefore, a long region such as the whole spine and the whole lower extremities cannot be covered by taking an image thereof only once.
Long region imaging is an imaging method of producing an image of such a long region. As disclosed in US 2004/0247081 A1, the number of times images are taken and the positions in which images are taken are determined according to the imaging region to be covered and the size of the FPD used, and the FPD and the radiation exposure field are moved along the examinee's body axis according to the determined imaging positions to take images (i.e., short images) in different regions a plurality of times, thereby producing an image of a long region covering the whole spine or the whole lower extremities. In long region imaging, short images thus taken are combined to obtain a long radiographic image of the whole spine, the whole lower extremities or the like.
Tomosynthesis imaging is an imaging method whereby a portion under examination is scanned by radiation in such a manner that the angle at which radiation hits the portion under examination is successively changed when carrying out successive imaging to produce a number of projection images, which are used to restructure a radiographic image of a desired tomographic plane.
Naturally, imaging methods as exemplified by long region imaging and tomosynthesis imaging, where a series of images are taken successively, take a longer time than normal imaging.
In addition, the examinee is required to stay motionless until imaging is completed.
In normal imaging, the examinee knows that a given imaging session has been completed when a single image has been taken (by a single exposure). However, in an imaging session such as long region imaging wherein a series of images are successively taken, the examinee is ignorant when the imaging session will end.
In addition, in the conventional radiographic imaging system, while the operator can be aware of the state of the system and the progress of the imaging session, the examinee remains ignorant of the progress of the imaging session.
Thus, in long region imaging, for example, the examinee is left totally ignorant of the time when the imaging session will end, the length of time it will take to complete the imaging session, and the progress of the imaging session and required to stay stationary and wait without being allowed to move until the operator gives an instruction.
Such conditions where the examinee is left ignorant of the length of time it will take to complete the imaging session and of the progress thereof and required to wait motionlessly causes anxiety to and produces psychological burden on the part of the examinee.
In particular, where the examinee is an elderly person or an individual with disabilities or where the examinee has suffered an injury such as a bone fracture, the examinee will feel a significantly great anxiety or psychological burden when he/she is required to hold still patiently even for a short period of time.